1. Technical Field
Example embodiments of the present invention relate in general to direct communication between user equipment (UE) and UE relaying, and more particularly, to a method of processing adaptive transmission and hybrid automatic repeat request (HARQ) of a device-to-device (D2D) link in order to perform direct communication between UE and UE relaying.
2. Related Art
Direct communication between UE is a communication method in which two adjacent sets of UE perform direct data transmission and reception without passing through a base station. In other words, the two adjacent sets of UE communicate as a source and a destination of data, respectively.
Direct communication between UE can be performed according to a communication scheme using an unlicensed band of a wireless local area network (WLAN), such as Institute of Electrical and Electronics Engineers (IEEE) 802.11, Bluetooth, or so on. However, in the communication scheme using such an unlicensed band, it is difficult to provide a planned and controlled service. In particular, the performance of the communication scheme may drastically deteriorate due to interference.
On the other hand, direction communication between UE provided by a wireless communication system using a licensed band or a television (TV) white space band employed in an environment in which interference between systems is controlled, can support quality of service (QoS), enhance frequency use efficiency through frequency reuse, and increase a communication distance.
On the other hand, UE relay communication is a communication method in which, to increase the transmission capacity of UE (UE A) present at a cell boundary or shadow region, neighboring UE (UE B) having a good link characteristic with a neighboring base station, that is, present relatively close to the base station or outside the shadow region, serves to relay data between the UE A and the base station. Here, the UE A may be a source and/or destination of the data.
Such UE relay can improve the transmission capacity of UE at a cell boundary, and also enhance the frequency use efficiency of a whole cell through frequency reuse.
The above-described direct communication and UE relay communication require a D2D link in common. A D2D link denotes a cellular communication method in which sets of UE belonging to the same cell or different cells exchange data through direct communication between them without passing through a network.
In the case of the direct communication between UE, only a D2D link is established between two sets of UE. In the case of the UE relay communication, a cellular link is established between the base station and the relay UE (UE B), and a D2D link is established between the relay UE (UE B) and the end UE (UE A).
To enable such direct communication between UE and UE relay communication in a current cellular communication system, problems relating to a HARQ and adaptive wireless transmission method between UE performing transmission and reception through a D2D link, etc. need to be solved.